US4057765A - Variable amplifier for RF input stage - Google Patents

Variable amplifier for RF input stage Download PDF

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Publication number
US4057765A
US4057765A US05/706,404 US70640476A US4057765A US 4057765 A US4057765 A US 4057765A US 70640476 A US70640476 A US 70640476A US 4057765 A US4057765 A US 4057765A
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United States
Prior art keywords
field effect
effect transistor
electrode
signal input
signal
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Expired - Lifetime
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US05/706,404
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English (en)
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Josef H. Schuermann
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Texas Instruments Deutschland GmbH
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Texas Instruments Deutschland GmbH
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    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G3/00—Gain control in amplifiers or frequency changers
    • H03G3/20—Automatic control
    • H03G3/30—Automatic control in amplifiers having semiconductor devices
    • H03G3/3052—Automatic control in amplifiers having semiconductor devices in bandpass amplifiers (H.F. or I.F.) or in frequency-changers used in a (super)heterodyne receiver

Definitions

  • This invention relates to a variable gain amplifier for RF-input stages comprising a field-effect transistor to which a control voltage is delivered.
  • gain is attenuated by means of the control voltage applied to a control electrode of the field effect transistor.
  • the drain current of the field effect transistor is reduced by the attenuation process. Attenuation is carried out in order to improve the large-signal behaviour and, in particular, the cross-modulation strength of the amplifier and the following stages.
  • An amplifier circuit functioning with a bipolar high-current transistor is also known, in which attenuation is effected by means of a PIN diode.
  • This PIN diode acts as an attenuator which attenuates the RF-signals arriving at the high-current transistor.
  • This circuit is also used for improving cross-modulation strength. Considerable outlay in terms of circuitry is involved in obtaining the necessary bias for the PIN diode.
  • cross-modulation strength curve obtainable by means of conventional amplifiers shows a generally increasing characteristic with increasing gain attenuation, it shows distinct dips where the cross-modulation strength is poor.
  • the object of the present invention is to design a variable amplifier of the kind referred to above in such a way that cross-modulation strength is considerably improved.
  • this object is achieved by virtue of the fact that a variable diode is arranged in the connection between the input electrode of the field effect transistor and the amplifier input, being biased in such a way that, when regulation begins, the field effect transistor is first attenuated by about 10 dB before regulation through the diode begins.
  • an RF-signal delivered to the amplifier input is initially attenuated solely by means of the control voltage delivered to the control electrode of the field effect transistor, i.e. this initial attenuation is not influenced by the variable diode.
  • variable diode is preferably a PIN diode which, in advantageous embodiments of the invention, is connected between the amplifier input and an input filter preceding the field effect transistor or between that input filter and the input electrode of the field effect transistor.
  • the bias of the variable diode is, in an advantageous embodiment of the invention, tapped from a source resistor of the field effect transistor and delivered to the anode of the variable diode through an RF-choke.
  • the field effect transistor may with advantage be an MOS-field effect transistor, operated as a common source circuit, and having two control electrodes, to the first of which the control voltage is delivered and of which the second is connected to the amplifier input through the variable diode.
  • the field effect transistor may also be an MOS-field effect transistor, operated as a common gate circuit, and having two control electrodes, to the first of which the control voltage is delivered and of which the second is at a fixed bias, the source electrode being connected to the amplifier input through the variable diode.
  • the field effect transistor is a barrier-layer field effect transistor operated as a common gate circuit, and having two control electrodes, to the first of which the control voltage is delivered and of which the second is at a fixed bias, the source electrode being connected to the amplifier input through the variable diode.
  • a clamp diode is connected to the source electrode of the field effect transistor in one advantageous embodiment of the invention, holding the voltage at the source electrode of the field effect transistor firmly at a predetermined value towards the end of the control range.
  • the clamp diode is with advantage biased in such a way that the predetermined voltage value, at which it holds the source voltage of the field effect transistor, is equal to or greater than the pinch-off voltage of the control electrode of the field effect transistor to which the control voltage is applied.
  • FIG. 1 is a graph showing the cross-modulation strength of a conventional amplifier and of an amplifier designed in accordance with the invention, as a function of the gain control;
  • FIGS. 2 to 5 show exemplary embodiments of a variable amplifier according to the invention.
  • FIG. 6 illustrates a circuit for generating an AGC voltage suitable for use in conjunction with an amplifier according to the invention.
  • the curve 1 represents a typical cross-modulation strength of a conventional variable amplifier equipped with a field effect transistor.
  • a cross-modulation strength such as indicated by curve 3, which represents a distinct improvement over curve 1.
  • FIG. 2 shows a variable amplifier circuit which may be used, for example, in the tuner of a television receiver.
  • This circuit contains, as its amplifying element, an MOS-field effect transistor 4 with two gate electrodes 5 and 6.
  • the usual AGC control voltage which attenuates gain by producing an increasing reduction in the drain current of the field effect transistor 4, is derived in conventional manner as illustrated by FIG. 6 delivered to the gate electrode 5 from the input 7.
  • the RF-signal to be amplified is delivered to the amplifier at the input 8 from which it passes through a coupling capacitor C1 to an input filter comprising the coil L1 and the capacitor C2.
  • the cathode of a PIN diode D1 is connected to the output 9 of the input filter, the anode of this PIN diode D1 being connected through a coupling capacitor C3 to the gate electrode 6 of the field effect transistor 4.
  • a potentiometer R1, R2 is connected between a supply voltage V+ and ground, the junction of R1, R2 being connected to the gate electrode 6 to apply a bias voltage thereto.
  • the source resistor of the field effect transistor 4 comprises two individual resistors R3 and R4.
  • An RF-decoupling choke Dr is arranged between the connecting point of the two resistors R3 and R4 and the connecting point between the diode D1 and the coupling capacitor C3.
  • a bias can be applied to the anode of the PIN diode D1 through this choke.
  • the cathode of a clamp diode D2 is connected to the source electrode 10 of the field effect transistor 4, A bias is applied to the anode of this clamp diode D2, from the tap of a voltage divider comprising resistors R5, R6 connected between V+ and ground.
  • the output signal of the amplifier is tapped through a coupling capacitor C4 from the coil L2 of an output circuit which is formed by this coil L2 and by a capacitor C5 and which is connected between the drain electrode 12 of the field effect transistor 4 and the positive terminal of the voltage source V+.
  • the value of the source resistor R3, R4 has to meet the following requirements: on the one hand, the value of this resistor should be high enough to ensure that a steep regulating effect is obtained through the voltage difference between the gate electrode 6 and the source electrode 10; on the other hand, it should not be so high that the current fed in to increase the source voltage produces an excessive voltage drop across the source resistor R3, R4 which would intolerably limit gain where only a limited supply voltage is available. To enable the value of the source resistor R3, R4 to be made sufficiently high without, at the same time, causing an unfavourable, excessive voltage drop across it, the voltage at the source electrode 10 is held firmly at a predetermined value by means of the clamp diode D2.
  • the voltage at the anode of the clamp diode D2 is adjusted to a value of 2.7 volts by means of the resistors R5 and R6. If, in the course of attenuation, the drain current of the field effect transistor 4 decreases and if the source voltage falls below 2.0 volts, the clamp diode D2 becomes conductive and delivers to the source resistor R3, R4 just enough current to ensure that the voltage value of 2 volts is maintained at the source electrode 10.
  • the drain current of the field effect transistor 4 decreases, the voltage drop across the resistor 4 falls below the threshold voltage of the PIN diode which is about 0.7 volt.
  • this fall can be made to occur after an attenuation of about 10 dB.
  • the PIN diode D1 then becomes highly resistive and acts like a current-controlled resistor which weakens the RF-signal.
  • the PIN diode D1 now also contributes towards attenuating the gain.
  • the field effect transistor 4 is initially responsible for attenuation, the clamp diode D2 providing for a favourable working range of the field effect transistor, enabling a distinct increase in the cross-modulation strength to be obtained in the vicinity of the dip A of FIG. 1.
  • the PIN diode D1 then begins to develop its regulating effect after an attenuation of about 10 dB, which considerably improves cross-modulation strength in the vicinity of the dip B of FIG. 1.
  • the amplifier with this control characteristic then produces the characteristic represented by curve 2 in FIG. 1 for the cross-modulation strength.
  • FIG. 3 shows another embodiment of the invention which differs from the embodiment illustrated in FIG. 2 solely in the fact that the PIN diode D1 precedes the input filter of the coil L1 and the capacitor C2. So far as its regulating effect is concerned, this embodiment behaves in exactly the same way as the circuit illustrated in FIG. 2.
  • the MOS-field effect transistor 4 in the embodiment illustrated in FIG. 4 operates as a common gate circuit.
  • the input electrode of the field effect transistor is the source electrode 10 to which the RF signal is delivered.
  • attenuation is initially obtained also in this circuit by the field effect transistor 4, whilst the regulating effect of the PIN diode D1 only begins after an attenuation of about 10 dB by the field effect transistor.
  • the MOS-field effect transistor is replaced by a barrier-layer field effect transistor (MESFET) 13 to whose signal gate electrode 14 the control voltage is applied.
  • This barrier-layer field effect transistor 13 is operated as a common gate circuit. Its source electrode 10 receives the RF-signal. So far as its regulating effect is concerned, this circuit also behaves in exactly the same way as the circuits described above.
  • variable amplifier described above has the advantage of minimal outlay on components, and when used in RF-input stages produces a significant improvement in large-signal behaviour. It enables the control range to be effectively utilised, which is of advantage particularly in cases where only a limited operating voltage is avaiable.
  • Suitable components for constructing a circuit as shown in FIG. 2 are as follows:

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  • Control Of Amplification And Gain Control (AREA)
  • Amplifiers (AREA)
US05/706,404 1975-07-25 1976-06-19 Variable amplifier for RF input stage Expired - Lifetime US4057765A (en)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
DE2533355A DE2533355C3 (de) 1975-07-25 1975-07-25 Regelbarer Verstärker für HF-Eingangsstufen
DT2533355 1975-07-25

Publications (1)

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US4057765A true US4057765A (en) 1977-11-08

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ID=5952486

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US05/706,404 Expired - Lifetime US4057765A (en) 1975-07-25 1976-06-19 Variable amplifier for RF input stage

Country Status (7)

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US (1) US4057765A (enrdf_load_stackoverflow)
JP (1) JPS5252352A (enrdf_load_stackoverflow)
DE (1) DE2533355C3 (enrdf_load_stackoverflow)
FR (1) FR2319241A1 (enrdf_load_stackoverflow)
GB (1) GB1550122A (enrdf_load_stackoverflow)
IT (1) IT1073966B (enrdf_load_stackoverflow)
NL (1) NL7608190A (enrdf_load_stackoverflow)

Cited By (10)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4131860A (en) * 1976-12-31 1978-12-26 Thomson-Csf Power amplifier arrangement automatically matched to service conditions
US4247954A (en) * 1978-03-01 1981-01-27 Saint-Gobain Industries Active window antenna for motor vehicles
US4393513A (en) * 1980-05-19 1983-07-12 Pioneer Electric Corporation Input signal level control device for receiver
DE3207945A1 (de) * 1982-03-05 1983-09-15 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Regelbarer hochfrequenzverstaerker
US4439741A (en) * 1982-06-28 1984-03-27 Motorola, Inc. Stabilized high efficiency radio frequency amplifier
US4737733A (en) * 1986-10-29 1988-04-12 Rca Corporation Overdrive control of FET power amplifier
US4806876A (en) * 1986-09-19 1989-02-21 Matsushita Electric Industrial Co., Ltd. High frequency amplifier circuit
US5126686A (en) * 1989-08-15 1992-06-30 Astec International, Ltd. RF amplifier system having multiple selectable power output levels
US20030179048A1 (en) * 2002-03-25 2003-09-25 Arild Kolsrud Amplifier bias system and method
WO2006079969A1 (en) * 2005-01-31 2006-08-03 Nxp B.V. Receiver having a gain-controllable input stage

Families Citing this family (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS5296851A (en) * 1976-02-09 1977-08-15 Matsushita Electric Ind Co Ltd Gain control unit
DE2911514C2 (de) * 1979-03-23 1982-07-15 Texas Instruments Deutschland Gmbh, 8050 Freising HF-Verstärkerschaltung
DE3626575C1 (de) * 1986-08-06 1987-10-15 Telefunken Electronic Gmbh Umschaltbarer Tunervorverstaerker
JPH0720970Y2 (ja) * 1988-07-04 1995-05-15 株式会社ケンウッド アッテネータ回路
DE4134177C2 (de) * 1991-10-16 1994-02-10 Telefunken Microelectron Schaltungsanordnung mit einer Dual-Gate-Feldeffekttransistor-Tetrode

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3428910A (en) * 1965-12-23 1969-02-18 Webb James E Automatic gain control system
US3525050A (en) * 1968-10-14 1970-08-18 Philips Corp Circuit arrangement for amplifying electric signals
US3624561A (en) * 1970-02-24 1971-11-30 Ben H Tongue Broadband aperiodic attenuator apparatus

Family Cites Families (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3482167A (en) * 1967-06-12 1969-12-02 Rca Corp Automatic gain control system employing multiple insulated gate field effect transistor
US3480873A (en) * 1967-12-11 1969-11-25 Rca Corp Gain control biasing circuits for field-effect transistors
DE1959782A1 (de) * 1968-12-23 1970-07-02 Be Dix Corp Veraenderliche Kopplungsvorrichtung fuer ein Radio-Empfaenger-System

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3428910A (en) * 1965-12-23 1969-02-18 Webb James E Automatic gain control system
US3525050A (en) * 1968-10-14 1970-08-18 Philips Corp Circuit arrangement for amplifying electric signals
US3624561A (en) * 1970-02-24 1971-11-30 Ben H Tongue Broadband aperiodic attenuator apparatus

Cited By (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4131860A (en) * 1976-12-31 1978-12-26 Thomson-Csf Power amplifier arrangement automatically matched to service conditions
US4247954A (en) * 1978-03-01 1981-01-27 Saint-Gobain Industries Active window antenna for motor vehicles
US4393513A (en) * 1980-05-19 1983-07-12 Pioneer Electric Corporation Input signal level control device for receiver
DE3207945A1 (de) * 1982-03-05 1983-09-15 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Regelbarer hochfrequenzverstaerker
US4439741A (en) * 1982-06-28 1984-03-27 Motorola, Inc. Stabilized high efficiency radio frequency amplifier
US4806876A (en) * 1986-09-19 1989-02-21 Matsushita Electric Industrial Co., Ltd. High frequency amplifier circuit
US4737733A (en) * 1986-10-29 1988-04-12 Rca Corporation Overdrive control of FET power amplifier
US5126686A (en) * 1989-08-15 1992-06-30 Astec International, Ltd. RF amplifier system having multiple selectable power output levels
US20030179048A1 (en) * 2002-03-25 2003-09-25 Arild Kolsrud Amplifier bias system and method
US7064613B2 (en) * 2002-03-25 2006-06-20 Lucent Technologies Inc. Amplifier bias system and method
WO2006079969A1 (en) * 2005-01-31 2006-08-03 Nxp B.V. Receiver having a gain-controllable input stage
US20090213276A1 (en) * 2005-01-31 2009-08-27 Nxp B.V. Receiver having a gain-controllable input stage
US8331893B2 (en) * 2005-01-31 2012-12-11 Nxp B.V. Receiver having a gain-controllable input stage

Also Published As

Publication number Publication date
DE2533355C3 (de) 1985-12-05
DE2533355A1 (de) 1977-01-27
JPS617765B2 (enrdf_load_stackoverflow) 1986-03-08
JPS5252352A (en) 1977-04-27
DE2533355B2 (de) 1980-03-27
FR2319241B1 (enrdf_load_stackoverflow) 1981-06-12
GB1550122A (en) 1979-08-08
NL7608190A (nl) 1977-01-27
IT1073966B (it) 1985-04-17
FR2319241A1 (fr) 1977-02-18

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